BOT3015L Symbioses

1. BOT3015LSymbioses Presentation created by Danielle Sherdan All photos from Raven et al.Biology of Plants except when otherwise noted

2. A continuum: Symbiosis Sym=together, bio=life A network of interactions among organisms on a continuum between beneficial and detrimental effects A major driving force behind evolution parasitism commensalism mutualism

3. A few examples • Flowering plants and pollinating animals • Humans and domesticated plants and animals • Humans and bacteria in their digestive system • Endosymbionts • Origination of mitochondria and chloroplasts

4. Example of endosymbiosis One cell containing numerous autotrophic algal cells Vorticella (protozoan) under compound light microscope ~5µm Scanning electron microscope

5. Basic Outline of (Primary) Endosymbiosisusing the plastid as an example Some debate about origin of outer membranes of plastids The bulk of evidence indicates that all chloroplasts resulted from a single primary endosymbiotic event (=monophyletic origin of plastids) involving cyanobacteria. Modified from Outlaw lecture

6. A few examples • Flowering plants and pollinating animals • Humans and domesticated plants and animals • Humans and bacteria in their digestive system • Endosymbionts • Origination of mitochondria and chloroplasts • Plants and bacteria • Rhizobia (also an example of endosymbiosis)

7. Bacteria Example effect on plant physiology Symbioses between plants and bacteria Many are parasitic, but Rhizobium is mutualistic

8. The bacterium enters the root and a nodule—part plant, part bacterium—is formed as a growth on the root. Legumes (and a few other plants) form a symbiosis with a nitrogen-fixing bacterium. RhizobiaSymbioses between plants and bacteriaNitrogen Fixation From Outlaw lecture

9. RhizobiaSymbioses between plants and bacteriaNitrogen Fixation Benefit to the plant: Source of usable nitrogen, which is limiting to growth. Benefit to the bacterium: Low O2 environment (O2 denatures nitrogenase) and source of reduced carbon. From Outlaw lecture

10. Flavinoids Liposaccharides Initiation of Rhizobium symbiosis at plant root 1. 3. 2. 4. 5. Modified from Outlaw lecture

11. Initiation of Rhizobium symbiosis at plant root Rhizobia (arrows) attached to young root hair Bradyrhizobium on soybean (Glycine) Scanning electron micrograph ~5µm

12. Initiation of Rhizobium symbiosis at plant root Root hair containing multiple infection threads (arrows) Bradyrhizobium on soybean (Glycine) Differential-interference contrast photomicrograph ~20µm

13. Initiation of Rhizobium symbiosis at plant root Infection thread with rhizobia Bradyrhizobium on soybean (Glycine) Scanning electron micrograph ~1µm

14. Initiation of Rhizobium symbiosis at plant root Groups of bacteroids surrounded by membrane derived from infected root cell (uninfected cell in the above adjacent cell) Bradyrhizobium on soybean (Glycine) Scanning electron micrograph ~2µm

15. Rhizobium symbiosis in dicot root nodule Cross section of mature root nodule. Rhizobia-infected cells are stained dark.Arrows indicate vascular bundles Bradyrhizobium on soybean (Glycine) Compound light microscope ~500µm

16. A few examples • Flowering plants and pollinating animals • Humans and domesticated plants and animals • Humans and bacteria in their digestive system • Endosymbionts • Origination of mitochondria and chloroplasts • Plants and bacteria • Rhizobia (also an example of endosymbiosis) • Humans and fungi • Leafcutter ants and fungi • Lichens

17. Lichens Symbiosis between fungus and population of unicellular or filamentous algal or cyanobacterial cells Caloplaca Reindeer moss (Cladonia) (note the misnomer) Interactions between lichens and animals exemplify the network nature of symbioses.

18. A few examples • Flowering plants and pollinating animals • Humans and domesticated plants and animals • Humans and bacteria in their digestive system • Endosymbionts • Origination of mitochondria and chloroplasts • Plants and bacteria • Rhizobia (also an example of endosymbiosis) • Humans and fungi • Leafcutter ants and fungi • Lichens • Plants and fungi • Mycorrhizae

19. Exposure to mycorrhizal fungi __ + Mycorrhizae Myco=fungus, rhiza=root • Fungus gets carbohydrates from plant • Plant gets better nutrient absorption • Both have protective effects on the other White pine (Pinus)

20. Endomycorrhizae endo=within Branched fungal hyphae (arbuscules) invaginate the plasma membrane of sugar maple (Acer) root cells Scanning electron micrograph ~10µm

21. EndomycorrhizaePawpaw and Glomales, an order of promiscuous endomycorrhizal fungi Fungi (stained blue to visualize) hypha arbuscules Plant cell wall The fungus does not penetrate the symplast. Modified from Outlaw’s lecture

22. Mycorrhizaedooryard observation Pawpaw (Asimina triloba) From Outlaw’s garden

23. Notice how much surface area is added by the fungus Ectomycorrhizae Fungus surrounds roots and grows between intercellular regions ~50µm Cross section of pine root with ectomycorrhizae Lodgepole pine (Pinus)

24. TodayInvestigating mycorrhizae: Comparative study of mycorrhizae in local plants Work in groups of 2-3 to stain, observe, draw, and describe mycorrhizae in at least 3 different plant species Draw and describe lichen and nodules without magnification, then section them, then draw them as they appear under the dissecting scope at a high magnification.